1. Field of the Invention
The present invention relates to a fluid-filled type engine mount designed to exhibit vibration damping action based on the flow action of a non-compressible fluid sealed therein, and more particularly to a fluid-filled type engine mount of novel construction furnished with a first orifice passage and a second orifice passage tuned to a higher frequency band than the first orifice passage, and able to produce vibration damping action against vibration in a multiplicity of wide frequency ranges.
2. Description of the Related Art
Engine mounts are known as components to be installed between a vehicle body and a power unit that includes an engine or other internal combustion engine, in order to provide vibration-damping coupling or vibration-damping support of the power unit on the body. One type of the engine mounts is a fluid-filled type engine mount that produces vibration damping action by utilizing the flow action, e.g. the resonance action, of a fluid produced when vibration is input across the mount. A mount of this kind comprises: a first mounting member and a second mounting member which are connected respectively to either the power unit or the body; a main rubber elastic body elastically connecting the first and second mounting members; a pressure-receiving chamber a portion of whose wall is constituted by the main rubber elastic body; an equilibrium chamber a portion of whose wall is constituted by a flexible film; and a non-compressible fluid sealed within this pressure-receiving chamber and the equilibrium chamber; and an orifice passage through which the two chambers communicate with each other.
Such a fluid-filled type engine mount is preferably able to produce excellent vibration damping action against vibration in a multiplicity of wide frequency ranges, in consideration of the existence of disturbances that could disrupt the prescribed operation condition and equilibrium condition. Particularly in the case of engine mounts for use in automobiles, since the frequency of input vibration to be damped can vary with driving conditions of the vehicle or other factors, the mount is required to function effectively to afford vibration damping ability of vibration in a multiplicity of wide frequency ranges. Specifically, it is a requirement that vibration damping action be produced, for example, against low frequency shaking vibration on the order of 10 Hz input during driving, as well as high frequency idling vibration on the order of 15-30 Hz input when the vehicle is at a stop.
In view of the problem discussed above, there have been proposed engine mounts that have a first orifice passage and a second orifice passage tuned to a higher frequency band than the first orifice passage. JP-A-10-132017, JP-A-8-4823, JP-B-7-54131, and JP-A 2001-336564 show examples of this type of engine mount.
In these engine mounts, there is disposed between the pressure-receiving chamber and the equilibrium chamber an intermediate chamber a portion of whose wall is constituted by a rubber elastic plate. The pressure-receiving chamber, the intermediate chamber, and the equilibrium chamber communicate with one another via a first orifice passage and a second orifice passage. With this design, the flow of the fluid induced to flow through the second orifice passage can be restricted by means of the rubber elastic plate during input of vibration in the resonance frequency range of the first orifice passage. This makes it possible to ensure flow of the fluid flowing through the first orifice passage. Also, by means of utilizing the resonance phenomenon of the rubber elastic plate during input of vibration in the resonance frequency range of the second orifice passage, fluid flow action of the second orifice passage can be actively actuated. This makes it possible to advantageously attain vibration damping effect based on flow action, e.g., resonance action of the fluid flowing through each orifice passage.
These engine mounts however have been suffer from a problem that when large vibrations are input across the first mounting member and the second mounting members, in some instances abnormal noise or vibration may be emitted by the mount. An investigation conducted by the inventors has shown that, in an automobile equipped with a fluid-filled type engine mount of conventional construction, abnormal noise or shock on a level that can be felt by passengers is sometimes produced in the cabin when the vehicle drives over deep corrugated pavement.